1. Field of the Invention
The present invention relates to a check valve for preventing backflow of a fluid, and more specifically to a check valve that opens when an expected fluid pressure is exceeded to thereby allow a fluid to flow toward the outlet side.
2. Description of the Related Art
In equipment in which a fluid is used, a check valve is used to prevent backflow of the fluid. For instance, many of feed water pipings used in water piping systems such as boilers are provided with a check valve to prevent backflow of feed water or boiler water. Boiler water has a high pressure and a high temperature, and it is therefore necessary, from the viewpoint of safety and the heatproof temperature of the pre-treatment equipment, that all possible countermeasures be taken against the backflow of the boiler water. To that end, it is necessary to take all possible measures to prevent leakage through the check valve (hereinafter also referred to as “check valve leakage”), that is, to prevent backflow of boiler water. As a measure for preventing such check valve leakage, various materials are used for a valve body that comes into abutment with a valve seat with a view to providing a complete seal between the valve seat and the valve body.
Examples of conventionally used valve bodies include an elastic valve body formed of an elastic material such as rubber and an inelastic valve body formed of an inelastic material such as metal, the latter being generally referred to as a metal seal. A check valve that relies solely on the elastic seal effected by an elastic valve body provides a good seal but is poor in pressure resistance and lacks in durability. Further, although a check valve relying solely on the metal seal effected by an inelastic valve body exhibits excellent pressure resistance and durability, even a trace amount of refuse caught between the valve seat and the valve body can cause so-called refuse clogging, which can easily impair the sealing property and make fluid backflow liable to occur.
In order to solve the above problems associated with a check valve, the applicant of the present invention has proposed a check valve including a valve chamber formed between a fluid inlet and a fluid outlet within a valve casing, a valve seat having a valve hole and formed on the fluid inlet side of the valve chamber, and a valve body provided within the valve chamber so as to be movable in the direction of fluid flow, the valve body being adapted to abut the valve seat from the fluid outlet side, wherein: the valve body is composed of an elastic valve body portion formed of an elastic material and an inelastic valve body portion formed of an inelastic material which is overlapped on the fluid inlet side surface of the elastic valve body portion and which is smaller in diameter than the elastic valve body portion; the valve seat is composed of a first valve seat portion with which the elastic valve body portion abuts and a second valve seat portion with which the inelastic valve body portion abuts after the elastic valve body portion comes into abutment with the first valve seat portion; the valve body is fixed to a valve shaft passing through a center of the valve body and having its both end portions supported by shaft support portions respectively provided on the fluid inlet and fluid outlet sides of the valve casing so as to be axially movable; and a spring for urging the valve body into abutment with the valve seat is interposed between the valve body and the support portion provided on the fluid outlet side (for example, see JP 2001-349454 A).
With this construction, a good sealing property is provided by means of the elastic valve body portion constituting the valve body, whereas high pressure resistance and durability are provided by means of the inelastic valve body portion, making it possible to obtain a check valve capable of effectively preventing a fluid backflow as compared with the check valve mentioned above, that is, the check valve that relies solely on the elastic seal effected by the elastic valve body or the check valve that relies solely on the metal seal effected by the inelastic valve body.
With the check valve disclosed in JP 2001-349454 A mentioned above, however, there is a fear that the outer peripheral portion of the elastic valve body portion which is in abutment with the first valve seat portion of the valve seat may undergo bending deformation as it is pushed toward the fluid outlet side by the fluid pressure of a fluid flowing into the fluid inlet side of the valve casing before that fluid pressure exceeds an expected pressure, that is, before the fluid pressure overcomes the elastic force of the spring interposed between the valve body and the support portion provided on the fluid outlet side, causing the outer peripheral portion to be detached from the first valve seat portion so that the fluid flows toward the outlet side. Further, the outer peripheral portion of the elastic valve body portion receives the fluid pressure of the fluid flowing in the valve chamber upon valve opening to thereby undergo bending deformation, causing a bent curl to form, which in turn leads to permanent deformation. This may impair the sealing property between the first valve seat portion of the valve seat and the outer peripheral portion of the elastic valve body portion at the time of stopping backflow, leading to check valve leakage, that is, fluid backflow.